These
insects are easily recognisable by their elongated snouts (this is known
as their rostrum). Weevils are also the bane of a gardeners
life as well, so they get everywhere. They are the commonest pest in stored
grain. The Grain Weevil cannot fly but is a tireless walker (should live
in the Lake District).

They
are usually found in grain storage facilities or processing plants, infesting
wheat, oats, rye, barley, rice, and corn. Although not often found in
the home, sometimes they infest table beans, acorns, chestnuts, birdseed,
sunflower seeds, and ornamental corn. They are rarely found in macaroni
and spaghetti (must have a thing about Italian food).

Identification:

Both
weevils have chewing mouthparts at the end of their snouts or prolonged
heads, and are about 1/8- to 3/16-inch long, depending on the size of
the grain kernel. In small grains, such as millet or milo maize, weevils
are small in size; they are larger in corn. The adult granary weevil is
a shiny reddish-brown with elongated pits on the thorax, whereas the adult
rice weevil is a dull reddish-brown with round or irregularly shaped pits
on the thorax and four light spots on the wing covers. These deep round
punctures and light spots are lacking on the granary weevil. Also, the
granary weevil cannot fly, whereas the rice weevil can fly. Both weevils
in the larval stage are legless, humpbacked, white to creamy white, with
a small, tan head. Weevils in the pupa stage have snouts like the adults.

Lifecycle:

The
egg, larva, and pupa stages of both weevils occur in the grain kernels
and are rarely seen. Feeding is done within the grain kernel, and adults
cut exit holes to emerge. Emergence holes of the granary weevil are larger
than those of the rice weevil, and tend to be more ragged than smooth
and round. Females drill a tiny hole in the grain kernel, deposit an egg
in the cavity, then plug the hole with a gelatinous secretion. The egg
hatches into a young larva which bores toward the center of the kernel,
feeds, grows, and pupates there. New adults bore emergence holes from
the inside, then leave to mate and begin a new generation. See the picture
below of weevils as they emerge.

Female
grain weevils lay from 36 to 254 eggs at a rate of 2-3 a day. At 80 to
86°F, 75 to 90% relative humidity, eggs hatch in wheat with a moisture
content of 13.5 to 19.6% in 3 days. Larvae mature in 18 days, and the
pupa in 6 days. The life cycle is about 30 to 40 days during the summer,
and 123 to 148 days during the winter, depending on temperature. Adults
live 7 to 8 months. Female rice weevils lay between 300 to 400 eggs, with
the life cycle requiring about 32 days for completion. Rice weevil adults
live 3 to 6 months, infesting grain in the field, especially in the tropics
and sub-tropics, in fact it is one of the most serious pests. Two larvae
can develop in one wheat kernel, but only one larva of the granary weevil
can develop per wheat kernel. Both granary and rice weevils feign death
by drawing up their legs close to the body, falling, and remaining silent
when disturbed.